STUDIES IN THE DRYING OF SOILS 



i 594 
K56 
opy 1 



A THESIS 

Presented to the Faculty of the Graduate School 

OF Cornell University for the degree of 

DOCTOR OF PHILOSOPHY 



BY 
MILLARD ALSCHULER KLEIN 



Reprinted from Journal of the American Society of Agronomy, Vol. 7, No. 2, 

March-April, 1915. 



In exchange 



JUK 



^8 '^^ 



Jv^^ 



f 



o 

^1 ti^^Reprinted from Journal of the American Society of Agronomy, Vol. 7, No. 2, 1915 i 



STUDIES IN THE DRYING OF SOILS.^ 

Millard A. Klein, 
Cornell University, Ithaca, N. Y. 

(Contribution from the Department of Soil Technology, Cornell University.) 

CONTEXTS. 

Page 

Introduction 50 

Reviev\^ of Literature .■« 50 

Experiment i, the Effect of Previous Drying of the Soil to Different 

Moisture Contents on Plant Food in the Soil and Plant Growth 54 

Soils Used 54 

Method of Experimentation 55 

Effect of Previous Moisture Content on Plant Growth . . . . 56 

Eft'ect of the Previous Moisture Content on the Morphological Char- 
acters of Wheat ; 56 

Effect of Previous Moisture Content on Crop Yield 5'"^ 

Eff'ect of Previous Moisture Content on Total Nitrogen in the Crop ... 60 
Eft'ect of Previous Moisture Content on Certain Constituents in the 

Water Soluble Matter in the Soil 61 

Total Solids 61 

Nitrates 62 

Potassium, Calcium, and Phosphorus 64 

Lime Requirements 66 

Summary 66 

Experiment 2, the Effect of Drying a Soil on its Physiological Con- 
dition as Measured by the Carbon Dioxid Production and Nitri- 
fication 67 

Carbon Dioxid Produced on Drying and Wetting a Soil 67 

The Effect of Drying and Wetting a Soil on the Nitrates and Nitri- 
fying Power 69 

Summary 7 ' 

Discussion and Conclusions 72 

Bibliography 75 

1 A thesis submitted to the faculty of the Graduate School of Cornell Univer- 
sity in partial fulfillment of the requirements for the degree of Doctor of Phi- 
losophy by Millard Alschuler Klein, B.Sc. Ithaca, N. Y-., February, 1915. Re- 
ceived for publication March 2, 191 5. 

49 



50 jourxat. of the american sociktv of agronomy. 

Introduction. 

The drying of tlic soil by exposure to intense sunlight fc^ some 
timt has been made use of in certain arid regions of India to increase 
its productiveness. Since the drying of the soil in an arid region has 
a stimulating effect on crop growth, it is to be expected that the lower- 
ing of the moisture content in soils of the more humid regions, during 
seasonable changes, will influence their ])roductiveness. The drying of 
tlie soil is a process that depends entirely on the climatic conditions, the 
degree and duration depending on the amomit and distribution of 
the rainfall in the region concerned. In a study of the increased pro- 
ductiveness due to drying it will be necessary to consider the changes 
in the physical, chemical, and biological conditions of the soil. 

The change in the ])lnsical condition of the soil due to drying may 
be^easily olxserved in the field. A better tilth is obtained as shown by 
an increased granulation. This increased granulation is to a great ex- 
tent due to the Hocculation of the colloidal material. 

The changes in the chemical composition due to drying have been 
studied by many investigators in relation to the amount of plant food 
recox'erable when a sample has lieen previously dried, untler various 
conditions and temperatures. Great differences in the amount of plant 
food recovered have been observed when a samj^le has been previously 
dried, which would show that the dr_\ing of the soil in the field may 
greatly influence the chemical com])osition. In the last decade much 
attention has Ijcen given to the biological changes which are taking 
place in the soil. Jn this C(jnnection drving has been considered as a 
l)artial sterilization, as the result:- liave lieen similar to those obtained 
from a ])artial sterilization witli steam or antiseptics. 

The great impo>rtance of the biological factors cannot be ignored in 
the stud)' of the <lr\-ing of the soil, but at the present status of soil 
investigation the\' must be studied in connection with the biochemical 
changes ])ro(luced. 

It is the purpose of the investigation to study the effect of drying a 
soil on crop yield and its correlation with certain chemical and phys- 
iological changes taking ])lace in the soil. 

Review of Literature. 

The successive drying and wetting of a soil greatly affects its phys- 
ical condition. 1"hese ])rocesses cause an increased granulation, re- 
ducing the size of the granules and forming lines of weakness and 
cracks, in many ways this {process is observed in the field but little 
data have Ijcen obtained experimentally showing the effect of succes- 
sivt; drying and wetting upon the physical condition. 



KLEIN: STUDIES IN THE DRYING OF SOILS. 51 

Wollny (1897)- stndied the effect of drying and wetting a soil on 
the volume change. The results show that a decrease in volume is 
obtained by drying and wetting. 

Cameron and Gallagher (1908) have shown that by repeated drying 
and wetting of a soil a point is reached where the volume on con- 
traction due to drying is equal to the expansion on wetting. This con- 
dition they call a " natural packing " of the soil. 

Fippin (1910) measured the effect of a repeated wetting and drying 
on clay soil by the force necessary to cause penetration. This force 
is reduced one half by five dryings and to one third by twenty dryings, 
granulation being increased Oo percent. 

The eifect of drying a soil has long been a problem to the soil chem- 
ist. Warington ( [882) recognized the im]x:)rtancc of drying a soil 
on the nitrate content. He found a reduction of nitrates in an oven- 
dried sample, a greater reduction when slowly oven-dried and an 
increase when air-dried. He advises drying a sample in a room, at 
55°-6o° F., for twenty-four hours as he foimd very little nitrification 
taking place at this temperature. 

Richter ('1806) dried a garden soil in an oven at 100° C, and foiuid 
an increase in tlie al)sor])tivc power for water and an increase in the 
nitrogen and solulile organic matter. 

The investigations of Iving (1905) on the amounts of plant food 
recoverable from field soils gives us the most valuable data on this 
subject. King compared the amounts of plant food recovered from 
fresh soil, soil air-dried, and soil dried in an oven at no'' C. He 
found more nitrates, phosphates, sulfates, bicarbonates, and silica, 
but less chlorides, recoverable from an oven-dried than from the fresh 
sample. The increase was greater than by washing the fresh sample 
with five times its weight in water. He considers that the increase 
may be partly due to the releasing of the salts locked up in the organic 
matter. .Knother cause may be what he calls the " fixing " power of 
soil grains, causing a concentration near the surface of the soil par- 
ticles which when dried are covered with the residues of evaporation 
and allow a greater solution than in the fresh soil. He also considers 
that the granular condition of the soil would allow a large, amount of 
water to be carried within the granules, the subse(|ucnt drying bringing 
the salts to the siu"facc and making them more accessible to solution. 

Leather (1912) found an increase in the nitrates in soils that had 
been dried in tlie sun at Pusa, India, the increase l)eing four times as 
.great as in the fresh sample. 

Kelley and McGeorge (1913) studied the efifect of drying on the 

- Dates in parentheses refer to bibliography at end of paper. 



5 2 JOURNAL OF THE AMERICAN SOCIETV OF AGRONOMY. 

mineral constituents of Hawaiian soils. C)n the average, drying the 
soils at loo" C. increased the water-soluble carbonates, phosphates, 
manganese, calcium, magnesium, potassium, aluminum, sulphates, 
and silica over the air-dried soil. The}- consider that the causes in- 
volve many factors, both chemical and physical, as flocculation, de- 
hydration, oxidation, and the altering of the film pressure. 

Investigations have shown that drying a soil has an effect on its 
biological condition. These changes must be studied in relation to 
the chemical changes produced and may be considered biochemical. 
Earlv bacteriologists considered that the soil was merely sterilized 
when heated. In recent investigations soils heated to temperatures 
lower than ioo° C. have been considered as partially sterilized. The 
(Irving of a soil ma}- therefore be considered as a partial sterilization. 

Russell and Smith (1905) find that nitrifying organisms can be 
easily killed b}- an insufticient amount of moisture or by drying at 
100° C. 

Rahn ( 1907) has made the most extensive investigations on the 
eft'ect of (Irving soils on their physiological condition. From studies 
on carbon dioxid and acid production in sugar solutions and ammonia 
production in i)eptone solutions he finds a greater bacteriological ac- 
tivitv in a soil previously dried at room temperature than in the same 
soil kept moist. Greater dift'erences were fmmd in a rich garden soil 
than in a sandy soil. The numlx'r of bacteria were decreased, and 
this he considers difiicult to explain if the effect is on the bacterial 
actixity. He believes that the eft'ect can not lie plnsical as an extract 
of the soil or a water suspension shows the same order of dift'erences; 
nor can it be the decomposition of the soil constituents because when 
j)hosphates and asjiaragin were added the same dift'erences resulted. 
Alustai'd grew better on a soil previousl}- dried. 

Pickering (lOoS) found that the heating of soils inhi])ited the ger- 
nfinalion of certain seeds, and that the alteration of the soil began at 
temi)cratures as low as 30" C. Xo appreciable destruction of the 
detriiuental substance occurred when the soil was kept for several 
months in a moderalel\- dry condition. 

I'urther experiments 1)}- Rickering (1008) show' an increase in the 
soluble organic material in soils heated to 30'^^ ()0°, and 80° C. and 
then exposed to the air for two months at summer temperatures and 
watered occasionally. At higher temperatures a decrease was obtained. 

Russell and Hutchinson (lojoi)) (1013) have studied the eft'ect of 
partial sterilization l)y heating with steam. They find an increased 
availaliility in plant food and an increased plant growth. This they 
believe is related to a change in the bacterial flora, the larger phago- 



KLEIN: STUDIES IN THE DRYING OF SOILS. 53 

cytic organisms being killed and the beneficial bacteria being allowed 
to increase. 

- Howard ( 1910) recognizes this etlect in the soils which are exposed 
to the intense sunlight of India. The fertility is increased, and he 
believes that this may be due to an inhibiting effect of partial steriliza- 
tion on the protozoa, as reported by Russell and Hutchinson on, the 
studies of soils heated in the laboratory. 

Russell (1910) recognizes the observation made by Howard and 
.believes that the soils exposed to sunlight may be dried and heated 
sufficiently to remove the factor which limits the productiveness of 
the soil. This is shown in further investigations by Russell and 
Hutchinson (1013). They exposed the soil to a temperature of 
35-38° C. for varying intervals. Upon remoistening the samples, it 
was found that the factor which is detrimental to the fertility is tem- 
porarily inhibited by ten days' drying. Soil exposed to sunlight for 
ten days behaves in the same manner. The detrimental organisms 
are killed at 55-60° C. and suft'er considerably at lower tempera- 
tures (40° C). They conclude that drying a soil has the same eft'ect 
as heating at low temperatures ; that is, it only temporarily eliminates 
the detrimental factor. 

Greig-Smith (1911) has shown that bacteriotoxins are destroyed 
at 04° C. He holds that upon remoistening the soil the more resist- 
ant bacteria multiply and become' more numerous because of the ab- 
sence of bacteriotoxins. Sunlight and air-drying the soil destroy the 
toxins. 

Ritter (1912) made studies similar to those of Rahn and found 
that bacterial activity increased on 'drying a soil. A dried soil gave 
quicker and more intensive action. " Heavy " soil showed a greater 
dift'erence than a " light " soil. A repeated drying and wetting caused 
a decrease in the activity. He concludes that the physical condition of 
a soil goes hand in hand with the physiological condition. 

Fischer (1913) discusses the work of Rahn and Ritter and com- 
ments oh their conclusions. He believes that more depends on the 
chemical composition than on the bacterial activity. Oxidation must 
be the principal factor, as the nitrates are increased on drying, yet the 
nitrifving organisms are killed. He thinks that colloids and surface 
tension must play an important part as a factor in this induced oxida- 
tion. 

Sharp (1913) studied the eft'ect of- drying by investigating soils that 
had been dried and kept in tightly stoppered bottl.es for thirty years. 
These soils still contained an average of 358,000 organisms per gram. 
Ammonifying organisms were present, but nitrifivcation occurred only 



54 JOURNAL OF THE AMERICAN SOCIETY OF AGRONOMY. 

feeliLy in two of the nine soils examined, llie nitrogen-tixing power 
was maintained l)ut the Azotobacter forms were absent in all except 
one soil. He concludes that there is no relation between numbers and 
physiological efficiency. 

]\ussell and Petherbridge (1913) found that plants grown on soils 
heated to 55° C\ show an acceleration in early growth succeeded by 
a steadv growlli. An increase in plant food in the soil and an in- 
crease in nitrogen, potassium, and phosphorus was found. 

Lyon and Bizzell (1913) found that the drying of the soil during 
seasonal moisture changes has both increased and decreased' the 
nitrates, dei)ending upon the kind of crop grown. In an unplanted 
plot an increase in soil moisture after a dry period has in most cases 
increased the nitrates in the soil. 

Experiment i. The Effect of a Prex'ious Drying of the Soil to 

Different 3iIoistuki". Contents ox Plant Eood in tuI': 

Soil and Plant (iRowrri. 

The object of the investigation i^ to suid}- the eitcct of drying the 
soil on its chemical and Ijiological condition and cju i)lant growth. 
l're\'ii)us inx'estigations on the drx'ing of the soil show that changes 
occur in the soil that greatly altect its ferlilit}-. That the effect is 
neither ])]iysical, chemical, nor biological, but a comliination of the 
three, has l)een generally acce])ted. 

In the held the soil is continualU" being subjected to an intermittent 
wetting an<l dr}ing. '^^1 he length of dryin.g aird the moi>ture content 
depend ui)on the amount and variation of the rainfall in the region 
concerned. 

In a humid region the period of drying is short and the moisture 
content to which the soil is dried is usually not \"er\- low. In an 
arid region the soil is sometimes air-dry or nearly so and remains dry 
for some length of time. 

AVith this in view tb.e plan of the experiment was to determine under 
controlletl condition^ tlie elTect of dr_\-uig the soil to dilTerent moisture 
conients on ])lant food in the soil and on plant growth. 

Soils Used. 

Two soils were used in the experiment, differing onl_\- iii organic 
matter. Soil No. i i-w a heavy clay loam known as Dunkirk clay loam. 
It contains comparatively little organic matter, but the fertility is 
good. Soil No. 2 is the samq type of soil, l)ut the organic matter had 
been greatly increased b}- ];)i!ing v.p timothy sod and allowing- it to 



KLEIN: STUDIES IN THE DRYING OF SOILS. 



55 



decompose. Some of the organic matter liad not entirely decomposed. 
This caused some difficulty in preparing the soil for the pots, as the 
uftdecomposed organic matter would tend to mass together. 

MctJwd of Ex pcvimcntation. 

The two soils were hrought in from the field December 9, 1911, thor- 
oughly mixed and put in 3-gallon pots. Each pot contained 1 1 kilo' 
grams of wet soil. A moisture determination was made at this time 
and the pots were brought to complete saturation (40 per cent). All 
pots were removed to the field-house January 11, 19 12. On Febru-ary 
28, 1912, the pots were brought in from the field-house. While the 
pots- were in the field-house the soil was frozen and a number of them 
were broken. The remaining pots were then allowed to dry in the 
greenhouse until they reached their permanent moisture content, as 
shown in Table i. 

T.-^BCE I.— The Moisture Content of Pots Used in the Experiment. 



Soil No. I. 



Series i, Unplanted. 



Pot No. 



Si-ries 2, Planted 
at 21; Percent. 



Conierrt. 



Soil No. 
Series i, Uiiplanted, j 



.Moisture 
Pot No. Content. 



Series 2, Planted 
at 25 Percent. 



Mcjisture 
ot No. Content. 



Percent. 



Pcrccnl. 



Percent. 



42 T 
422 
424 
4^5 
426 
427 
428 
429 



30 
30 



40T 
403 
408 
411 
412 
430 
415 
416 

417 
41 8 
419 
420 



30 
30 
30 



447 
448 
449 
450 
4.St 
4.S2 
4. S3 
454 
45. S 
45f) 
457 
458 
459 
460 



40 
40 





Per cant 


431 


15 


432 


TS 


433 


I3 


434 


20 


435 


20 


436 


20 


437 


25 


438 


■?5 


439 


25- 


440 


,^0 


44 T 


30 


442 


30 


443 


40 


444 


40 


44.5 


^ 



The pots of the highest water content were at saturation. In soil 
No. I the highest water content was at 35 percent, but ajter a few 
months the water stood on the surface of the soil and it becajiie neces- 
sary to drop this water content to 30 percent. Just the opposite con- 
dition was found in soil Xo. 2, and the highest water content of 35 
percent was raised to 40 percent. The moisture content as showm tn 
Table i gives this corrected percentage for the pots kept at saturation. 

The pots were kept at the difl'erent moisture contents as shown in 



56 JOURNAL OF THE AMERICAN SOCIETY OF AGRONOMY. 

Tabfe i until December 19, 1912. They were then divided in two 
series. One series was prepared for planting by bringing all pots to 
25 percent moisture content, while the second series was kept bare 
at the ditterent moisture contents. The division of the pots in two 
series is shown in Tal)le i. 

On January 14, 1913, all pots of series i were planted to Galgalos 
wheat. Fort}' seeds were jdanted in each pot. A good germination 
was secm"ed and the seedlings were thinned to 12 plants. 

.,'Effcct of Previous Moisture Coufenf on Plant GroictJi. 

At all early stage soil No. i allowed a Ix'tter growth. On April 29, 
1913, the pots that had been previously held at a high moisture con- 
tent showed a ])Oorer growth than tliose held at a low moisture con- 
tent.' At th.e lime of heading the plants in pots 440, 441, and 442 
were 'much smaller than others of the same series. Un June 4, the 
plants in pots 437. 43S, and 439 were making the best growth. 

On Ala}- 22, it could l)e seen that the drying out of a soil to a low 
moisture content ])revious to planting was having a Ijeneficial eiTect 
on plant growth. In soil Xo. 2 the pots which had been held at 30 
percent moisture content previous to planting showed a poorer growth 
than the ones ])reviously held at 40 percent. 

A more luxuriant growth was ol:)tained <.)n soil 2, the great dif- 
ference evidently being due to the greater amount of organic matter 
in soil No. 2 or to some factor depending upon the organic content. 

On June 17, the plants were fully headed but were not entirely ripe. 
It was necessary to harvest on this date, however, owing to attacks 
made upon the plants !))■ rodents in the greenhouse. The plants on 
soil No. I were somewhat nearer maturit\- than those on Soil No. 2. 
The plants from all pots were hung in the greenhouse and allowed to 
ripen completelw 

Alillet was immediately planted, but a very poor growth of the 
seedlings was obtained. It was therefore replaced by buckwheat. 

The pots containing soil No. i had become so compact that it was 
necessary to lower the water content from 25 percent to 22 percent. 
During the growth of the buckwheat little difference could be ob- 
served. It was evident that the' pots had reached a point where the 
previous moisture content had little eiTect. or that buckwheat was not 
appreciably affected by changes in the moisture coiitent. 

Effect of Pre7'ious Moisture Content on tJie Morp]ioJo(i\ of'JJlieat. 

A study of the eff'ect of drying a soil to different moisture contents 

on the morphology of wheat is shown in Table 2. The results with 



KLEIN : STUDIES IN THE DRYING OF SOILS. 



57 



soil No. I do not show a' great ditTerence in the first three water 
contents (15. -20, and 25 percent). A great decrease will be noted in 
pots 418, 419, and 420 in the nunil)er of culms per pot, but only a 
slight difference in the other characters. These pots were held at 
saturation before planting and a poor physical condition of the soil 
was notic&able. 

Table 2. — Effect of Previous Moisture Content on the Morphological Characters 

of -Wheat, 



1 P''^" 

1: vious 
Pot No. I Moist- 
jUre Con- 
tent. 



Culms 
per pot 

(12 
Prants). 



Length of 
Culm. 



Length of 
Head. 



per 
Head. 



Empty |,^P')^.t 
Spike "*" "" 



lets with 

one 
Grain. 



Spike- 
lets with 



Spike- I Nodes 
lets per 

t\^'° (Total.) Culm. 



Grains 













Soil No. I 


















P. Cl. 




Inches 


Inches 














401 


15 


25 


34-7 


3-08 


16.8 


2 


8 


7.2 


4.8 


— 


4.0 


403 


15. 


25 


34 


7 


3.00 


13-4 


3 


4 


7.0 


4 





— 


3-7 


408 


15 


25 


37 


3 


3-30 


16.5 


2 


7 


6.0 


5 


2 


— 


2,-?, 


Ave. 


15 


25 


35 


6 


3-12 


16.0 


3 





6.7 


4 


7 


14.4 


3-7 


-411 


20 


26 


33 


5, . 


3.20 


15-4 


2 


3 


7-1 


4 


2 


— 


3-9 


412 


20 


20 


42 


5 


3.20 


1.7-0 


2 


4 


6.5 


5 


I 


— 


4.0 


430 


20 


26 


36 


6 


3.20 


16.3 


3 


I 


7.0 


4 


8 


— 


3-9 


Ave. 


20 


24 


3-7 


5 


.3-20 


16.0 


2 


6 


6.8 


4 


7 


14.1 


3-9 


415 


25 


25 


34 


8 


2. So 


14-7 


2 


5 


7.0 


4 


I 


— 


4.0 


■ 416 


25 


22 


35 


3 


3.00 


13-8 


3 





7-r 


3 


3 


— 


3.0 


417 


25 


19 


34 


0- 


2.80 


. 13-0 


3 





7.0 


3 


2 




3.6 


Ave. 


25 


22 


34 


7 


. 2.95 


14.0 


2 


8 


7.0 


3 


5 


13-3 


3-7 


418 


30- 


12 


31 


3 


2.40 


I0-.5 


3 


3 


6.3 


2 





— 


4.0 


419 


30 


13 


34 


5 


2,50 


12.0 


2 


Q 


6.1 


3 





— 


3-7 


420 


30. ^ 


13 


31 


6 


2.45 


10.3 


I 


6 


6.3 


2 


2 


— 


3-5 


Ave. 


30' ^ 


13 


35 


8 - 


■ 2.45_ 


• II. 


2 


5 


6.2 


2 


4 


II. I 


3.7 











Soil Nor 2 
















431 


15 


36, 


30.5 • 


3.36 


19.0 


2.6 


5-4 


,6.4 


— 


34 


432 


15 


34 


30.3 


3-56 


18.3 


2.4 


6 





6.3 


— 


3 


5 


433 


IS 


44 


34-4 ■ 


3-40 


17.0 


2.5 


5 


3 • 


5-8 


— 


3 


5 


Ave. 


15 


38 . 


- 31-7 


3-40 


18. 1 


2-5 


5 


6 


6.2 


14-3 


3 


5 


434 


20 


30 


28.5 


3-20 


14.1 


2:2 


5 


2 


6.0 


— 


3 


7 


435 


20 


34 


29.(1 


■ 3-20 


16.8 


2.2 


5 


5 


5-5 ■ 


— 


3 


5 


4J6 


•20 


34 


30.0 


3.60 


16.9 


2.0 


5 





7.3^ 


— 


3 


5 


Ave. 


20 


33 


29.4 


3-30 ' . 


15-9 


2.1 


5 


2 


6.3 


13.6 


3 


6 


437 


25 


33 


32.4 


3.60 . 


18.6 


2.0 


5 


2 


6.6 


— 


3 


7 


438. 


25 


35 


30.6 


3-40 


18.5 


2.0 


6 





6.3 


■ — 


3 


6 


439 


25 


27 


34-3 


■ 3-40 - 


16.6 


1-7 


5 


2 


0.5 


• — 


3 


9 


Ave. 


25 . 


32" 


32.4 , 


3--50 


i7;-9 


1.9 


5 


5 


6.5 


13-9 


• 3 


7 


440 


30 


17 


34,2 


. 5-40 


17-7 


2.1 


4 





6.7- 


— 


. 3 


6 


441 , 


30 


17 


23.2 


2.50 


13.0 


2.3 


4 


4 ■ 


4.4 


— 


3 


2 


- 442 


k30 


13 


S2.^ 


.2:30 • 


9.0 


_3-5 


5 





2.0 


— 


3 





Ave. 


30 


16 


26.7 


2.70 , 


13-2 


2.6 


4 


5 


4-4 


II-5 


3 


3 


• 443 


40 


34 


27.7 


3.00 


14-5 


•2.4 


6 


5 


4.0 


— 


3 


3 


.444 


40 


41 


■ 30.0 • 


■ 3-10 


i8.-f 


?-7' 


6 


2 


• 6.0 


— 


3 


7 


445 


40 


41 


30.3 


3-40 


16.8 


3-2 


6 


2 


5-2 


— 


3 


5 


Ave. 


40 ' 


38 


29-3' 


3-20 


16.8" 


2.8 


6 


3 


5-1 


14.2 


3 


5 



1 Also 5 three-grained spikelets. ■ 
- Also 7 three-grained spikelets. 



58 JOURNAL OF THE AMERICAN SOCIETY OF AGRONOMY. 

Ill soil No. 2, gTcater (iitferences in the nioi'phological cliaractcrs 
due to tlie eflecl: oi the previous uioisture content could be noted. 
Here, as in the plant growth, tlie soil that had been held at 30 per- 
cent moisture content shows the poorest results. There is a similarity 
between the ])()ts which had been held at 15 percent and those at 40 
percent, the average numl)ei" of culms per pot being as great in the 
40 percent as in the 15 i)ercent pots. 

Comparing the two soils, we iiixt a greater number of culms per pot 
in soil No. 2, Init the length of culms is sonienvhat less in this soil. 
'^Jdie greater nunil)er of spikelets with one grain were found on the 
plants in soil No. i, and the greater number with two grains were 
found on the plants in soil No. 2. It will be seen that in soil No. i there 
was a decrease in the number of grains per head as the moisture 
content was increased, whila in soil No. 2 there was little diti'erence 
as aFfectetl by the ditTerent moisture contents. 

Rffcct' of J'l-crioiis Mcnshirc Cuiitciit o)i Crof^ Yield. 

A large nunil)er of investigators have studied the effect of ditTerent 
moisture contents on croj) yieUL '.riiey do uo[, however, consider the 
possil.)le iniluence of the moisture condition of the soil before planting. 

]n this in\-estigation the soil A\'as kept at the different moisture con- 
tents for ten months l)efore ])Ianting. At the time of i)lanting all pots 
were brought to an optimum water conttnit and the weights recorded. 
During plant growth the ])ots were kept at tlvis content by adding dis- 
tilled water e\ery day and bringing the pots to standard weight, 
Lnder this jjlan an)- ditlercnces in the ajnount of dry matter produced 
in the crop nuist l)e due to the. effect of the previous moisture con- 
tent and not to differences during the gTowth of the plants. 

As the two soils differ only in organic content, a comiiarison'of the 
results should show the inliuence of organic matter on the factors 
eflecting tlie previous drying out o-f a soil io various moistrtre contents. 
The ehcct ot the previous condition* of soil moislui'e on tire produc- 
tiim 01 iuy matter is shown in Table 3. 

In soil No. I, the greatest weig-ht of dry matter in the first c.rojD, 
botii grain and straw", is foiuKl in the -'^oil that bad l)ecn pre.viou,s!y 
dried to 15 ])ercen!., a somewhat: snialler yiekl at 20 percent and at 
2^, ])ercent. an<.l a decided decrease at 30 pcrcejit. The sail that w'as 
held at 30 percent was reduced to 25 percinifat the time of jdantrng". 
The same order of dilTereiices was fomid in soil No. 2, cxce]5t that 
when 40 percent is re^ached there is a decided iticr.ease over the 30 
])crcent. In this series the .soil that was held' at 40 percent was re- 
duced io J5 pci-ccnt at the time of drying. 



KLEIN: STUDIES IX THE DRYINC OF SOILS. 



59 



111 soil No. 2, a moisture content of 40 percent must be compared 
to the content of 30 percent in soil No. i, as in both cases we have 
complete saturation for each soil. In the clay loani pots which had 
been previously held at saturation the yield of dry matter is smallest, 
but in the organic clay loam pais which had been held at saturation 
the yield is as large as those with the lowest moisture content. If 
we consider that the lowering ot the moisture content in the pots at 
40 percent moisture content is an effective drying out previous to 
planting, there is decided increase due to drying just before planting. 

T.\BLE s.—EjJccl of Previous Moisture Cotitcni on Weight of Dry Matter of 
Wheat and Buekn'Iieat Frodueed. 







SoR-No. 


I. 






Previ- 
ous 


Soil No. : 
Wh 


eyt. 






Previ- 
ous 


Wheat. 








Pot No. 


Mois 
ture 






]!ucl:- 
uheat. 


Pot No. 


Mois- 
ture 






wheat. 












CoB- 
ttnt. 


Grain. 


Straw. 






("on- 
tem. 


( Irainr. 


Straw. 






P. a. 


Grams 


drains 


Grams 




P. a. 


Grams 


Grants 


Grams 


401 


15 


IS. 2 


30.3 


5-9 


431 


15 


20.5 


42.3 


_ 8.8 


403 


^ 15 


17-4 


2S.7 


4.5 


432 


15 


17.0 


39.0 


9.0 


408 


15 


ig.i 


31.8 


4-7 


433 


15 


23.2 


45-7 


9.4 


Ave. 


15 


18.2 


30-3 


4-7 


Ave. 


15 


20.2 


42.3 


9.1 


411 


- 20 


18.5 


29 -.1 


4-5 


434 


20 


15-8 


30.6 


9.0 


412 


20 


15-8 


26.6 


4.9 


435 


2a 


16.3 


34-5 


9.6 


430 


20 


20.0 


33-2 


4.0 


436 


20 


21.7 


42.5 


9-5 


Ave. 


20 


18 I 


29. 8 


4-5 


Ave. 


20 


17.8 


'35-9 


9-3 


41S 


25 


16.6 


27.0 


4.0 


437 


25 


15.8 


41-9 


9.9 


416 


25 


1 3 


25.1 


4.0 


438 


25 


x6.S 


40.1 


10.8 


417 


25 


11.4 


20.6 


5-.S 


439 


25 


14-4 


33-9 


9.2 


Ave. 


25 


14.0 


24-3 


4-5 


Ave. 


25 


15-5 


38.6 


9-9 


4-1 8 


30 


4.9 


1 0.0 


— . 


440' 


30 


8.8 


22.1 


8.0 


419 


30 


5.2 


12.5 


(X.2 


441 


->" 


S-~ 


11-3 


7-4 


4 2 a. 


30 


6-3 


" r2.7 


0.3 


442 


30 


2.4 


1-1 


7.2 


Ave. 


30 


.>-5 


II. 7 


^i-3 


Ave. 


30 


5-5 


13-7 


7-5 












443 


40 


14.6 


28.6 


9.0 












4-44 


40 


22.9 


46-5 


10. 












445 


40 


20.2 


41.0 


10.8 












Ave. 


4Q 


19.3 


38.6 


9-9 



This, however, is not the case in the 30 percent moisture content pots 
which have alscr been lowered to 25 percent before planting. 

The eiTect of drying to lower moisture contents previous to planting 
has been to increase the crop yield, as is conclusively shou-n in soil 
No. I and also in sorl No. 2, if the lowering of the 40 percent moisture 
content l^efofe planting \yc so considered. 

With the second crop, Inickwheat, there has been little effect. There 



6o 



TOI'RX-\L OF THE AMERICAX SOCIETY OF AGRONOMY. 



h, however, a greater increase in the yield of soil No. 2 over soil No. 
I than in the first crop. 

Effect of l^rcz'ioiis Moisture Content on tJic Total Nitrogen in the 

Crop. 

The results ol)tainecl in the determination of the total nitrogen in the 
dry matter of the grain and straw are shown in Table 4. It has been 
repeatedly shown that plants grown under different moisture condi- 
tions show a variation in the amotmt of plant constituents found in the 
dry matter. A greater crop growth usually causes a smaller percent- 
age of nitrogen in tlie i)lant. (hi the other hand, if the available 
nitrogen in the soil is increased l)y an increase in the moisture con- 
tent, an increase may be found in the percentage ()f nitrogen in the 
crop. The chemical constituti(3n of the soil niust be a factor, more 
'especially in the soluble organic matter. 



Table 4. — Effect of Previous Moisture Coutcut 011 Total Nitrogen in the Crop. 



Soil No. I. 


Soil No. 2. 




w^ 


Total Nitrogen. 




.2 „• 


Total Nitrogen. 


y. 


-1 


Wheat. 


Buckwheat. 




y. 


3* ^ 

e5 il 


Wheat. 


Buckwheat. 


~ 


5 


1' i ^ i 


Total. 
Ratio. 


- 


f 'J 
> 'J 


c 


Raiio. 
Straw. 
Rati,>. j 


• - 1 .5 




Per- 


Pa- Per- 




Per- 




Per- 


Per- 


Per-\ 


Per- 




cent. 


cent, cent. 


cent. 




cent. 


cent. 


cent: 


cent. 


401 


15 


1.40 — .27 


— 


1.63 — 


431 


15 


3.26 


— 1.02 — • 


2.07. — 


403 


15 


1.68 — .26 — 


1.62 — 


432 


15 


3-30 


• — 1 . 1 3 ■ — ■ 


2.25 — 


408 


15 


1.60 — .25 — 


— 


— 


433 


15 


3.26 


— I . I S — 


1.84 — 


Ave. 


IS 


1. 59 100 .26 


100 


1.63 


100 


Ave. 


15 


3-27 


100 I. II 100 


2.05 100 


411 


20 


1.73 — .26 


— 


1.74 


— 


434 


20 


3-24 


— 1. 17 ' — 


2.:50" 


412 


20 


1.60 — .26 


— 


1.82 


— 


435 


20 


3.25 


— 1. 16 — 2.10 — 


430 


20 


1.48 — .29 


— 


1. 81 


— 


436 


20 


3.26 


— .95 — 2.04 — 


Ave. 


20 


1.60 100 .27 


103 


1.79 


109 


Ave. 


20 


3-25 


99 1.09 98 1 2. 15 104 


41S 


25 


1.6^ — .26 


— 


— 


— . 


437 


25 


,3-32 


— ;i.i5 — 


2.09 


416 


25 


1.67 — .25 


^- 


1-45 


— 


438 


25 


.? • 2 7 


— 1.18' — 


2.15 — 


417 


25 


1.72 — .27 


— 


1.62 


— 


439 


25 


3-43 


— 1. 12 — 


2.18 


Ave. 


25 


1.67 104 .26 


100 


1-53 


94 


Ave. 


25 


3-34 


102 I. IS 103 


2.14 104 


418 


.30 


1.88 — .30 


— 


1.66 


■ — 


440 


30 


3.06 


— Leo — . 


2.35 — 


419 


30 


I-7I — -39 


— 


— 


— 


441 


30 


2.88 


— ■1.60 — 


2.40 


420 


30 


t.53 — .28 — 


1. 7 1 


— 


442 


30 


3.26 


— 1.60 ;— 


2.42 — 


Ave. 


30 


1. 71, 107 .32 


107 


1. 68 


103 


Ave. ■ 


30 


3-07 


93 .1.60 '' 145 ; 2.39 116 
















443 


40 


3.36 


— 1.25 ! — I 2.22 — 












1 ■ ■ 


444 


40 


3.3 1 1 — .88, — 


•i.5fi. — 












^ 


445 


40 


3.34 ■— .92 J, — 


1.4') — 










1 


Ave. 


4'J 


3.34 102 1. 01 91 t.4() 71 



KLEIN: STUDIES IN THE DRYING OF SOILS. 6 1 

The results presented in Table 4 showthat there has been no effect 
on the nitrogen of the crop resulting from a dift'erence of the previous 
moisture content. A comparison of the two soils shows on the aver- 
age twice as much nitrogen in tlie plants grown in the soil high in 
organic matter as in the same soil low in organic content. As these 
soils differ only in organic content and the results sliow practically no 
difference due to water content, the dift'erence in the percentage of 
nitrogen in the dry matter must be caused through some factor due to 
the organic matter. 

Effect of Previous Moisture Content on U'ater Soluble Matter. 

It has been shown by a numljer of investigators that the complete 
drying of the soil causes an increase in the soluble salts recoverable 
from a water extract. However, in this investigation the soil has in no 
case been dried to an air-dry condition. 

The results presented in Table 3 show that a lowering of the mois- 
ture content previous to planting has caused an increase in the plant 
growth. In order to determine whether this increase was related to 
an increased amount of plant food, determinations were made on the 
total solids, nitrates, potassium, and calcium in the water extract and 
phosphorus in a fifth-normal acid extract. 

It might be expected that the greater plant growth in the soil high 
in organic matter would result from the large amount of plant food 
carried in the organic material. Water extracts were made from 
soils from all the pots immediately after the second crop was har- 
vested, by adding 500 c.c. of distilled water to 100 grams of the soil 
and filtering through a Pasteur-Chamberlain water filter. 

Total Solids.- — Tal)le 5 shows the results obtained in the determina- 
tion of the total solids frOm a water extraction of the soil sample. It 
will be seen from this table that low water content reduces the total 
solids in the unplanted clay loam, while in the planted series of this 
soil there is little dift'erence in the results. The results with the soil 
high in organic matter show an increase in the total solids in both the 
planted and unplanted series with an increased moisture content. 

Considering the effect upon the clay loam, it is evident that drying 
the soil to a lower moisture content has increased the water-soluble 
matter. The planted series of this soil shows this same increase, 
although at the time of planting all pots were brought to the same 
moisture content. The opposite eft'ect in the organic clay loam must 
be attributed to the greater amount of organic matter. It is evident 
that the lowering of the moisture content has had no effect on the total 
solids recovered, as the amounts increase with ' the increased water 
content. 



62 



TOfRNAL OF THE AMERICAN S0CT1<:TV OF AC.RONOMY. 



Table 5. — Rffcct of Prcrious Moisture Content on Solulilr Salts in the Soil 
(Total Solids in Water Extract Expressed in Parts per Million). 



Soil No. I. 
Series i. I'lantcd. Series 2, Fnplanted. 






o'-" 



Serii-s I, Planted. Series 2. Unplanted 



401 


i.S 


390 


■ — 






403 


i.S 


305 


— 


421 


1.5 


408 


I.S 


402 


— 


422 


15 


Ave. 


15 


^3b 


100 


Ave. 


15 


411 


20 


408 


— 






412 


20 


37-' 


— 


424 


20 


4.-?o 


20 


440 


— 


425 


20 


Ave. 


20 


406 


120 


Ave. 


20 


41. T 


2.S 


329 


-- 






410 


2$ 


344 


— 


426 


25 


417 


~5 


— 


— 


427 


25 


Ave. 


25 


3.1^^ 


91 


Ave. 


25 


418 


30 


366 








419 


30 


362 




428 


30 


420 


30 


320 


■ — 


429 


30 


Ave. 


30 


350 


95 


Ave. 


30 



94 



874 
800 
837 



890 
690 
790 



666 
464 
5f'5 



523 — 
S26 — 
525 6: 



43 T 

432 
433 
Ave. 

434 
435 
436 
Ave. 

437 
438 
439 
Ave. 



J . 














c 


J^ 






-ii 3 


XI 




<< i 


•- 




z 


.« 2i 


" 




=•3 


■s. 


■= 


Z 


y 


f: 


■5 


■> V 




« 


P-, 


> ^ 




'~ 






































Oh " 






15 


517 


— 


447 


15 


1226 


— 


15 


704 


— 


44S 


15 


747 


— 


15 


43« 


— 


449 


IS 


1510 


— 


15 


553 


100 


Ave. 


IS 


1198 


100 


20 


915 


_ 










20 


687 


— 


451 


20 


882 


— ■ 


20 


473 


— 


452 


20 


2222 


— 


20 


691 


124 


Ave. 


20 


155" 


13 1 



7O0 — 453 25 1613 — 

870 — 454 25 1584' — 

746 — 455 25 13231 — 

792 j 143 Ave. 25 15071 127 



440 , 30 941 — 456 I 30 1456 

441 30 960 I — 457 ' 30 I3<''4 
j^.\2 30 605 — 458 I 30 12352 
A\-e. 30 835 151 Ave. 30 1724: 146 

443 4» 741 ; — 459 ' 40 24501 — 

445 40 938 ! — 460 40 1467' — 

Ave. 40 863 \ 156 Av. 40 '180S 153 



It would seem lliat ihe loweriiit,^ of the water eontent as affecting 
the \vater-soliil)le jna.tter depends entirel}' u])(>n tlie t_\i)es of soil used. 

X It rates. — In order to ascertain what effect the lowei'ing of the 
nioi-ture content may ha\e upon the nitrification in the soil, the nitrates 
were determined on sami)les from all the pots after the second crop 
had heen har\-ested. The sami)!es were brought to the laboratory 
and the moisture and nitrate determinations were made within sixteen 
hours after sam])ling. The nitrates were determined colorimetrically 
by the phenol disnlphouic-acid method. The results are presented in 
'J"able 6. 

If a com])arison of series i and 2 of both .soils is made it will be 
seen that a reduction of the nitrates was caused by ])lant growth. The 
ana.ly^es also show that the nitrate^ are le>s in the planted series of 
soil No. I than in the same series cif soil Xo. 2. d his may be due 
to the greater amount of nitrates present in the organic clay loam he- 
fore planting, there being more tlian necessary to satis f\' the require- 



KLEIN: STUDIF.S IN THE DRVINC, OF SOILS. 



•63 



ments of the plants. From Tallies 3 and 4 it will be seen that a 
grealer growth and a greater amount of total nitrogen in the crop 
were obtained in the organic clay loam. A decrease -is found in the 
nitrates of the planted series due to the i)revi()us lowering of the 
moisture content, this decrease being more decisive in the clay loam. 
Under the unplanted series of both soils the results would tend to show 
that there has been little effect on the nitrates duo to a lowering of the 
moisture content. A reduction may be expected in the planted scries, 
as pots at the previous low moisture contents gave much greater 
growth. 



Table 6. — Effect of Previous Moisture Content on Nitrates in the Soil. 









5oiI X 


>. I. 






ted. 




Soil No. 2. 






Series i. P 


anted 


Series 2. L 


nplan 


Se 


ries I, Planted. 

i s 'J y< " 


Ser 


es 2, L 


nplanted. 


Z 


i ^ ? 


2 
. Z 

p.p. 


1 


S: .2 2 § 


•h 


iA 


Previous 
Mni.sture 
Coiuent. 


Z ~ 




P.p.\ 




p.p. 


p.p. 




P.cl. 


m. 




p.cl. 


m. 




P.cl. m. 




P.ct. 


m. 


401 


15 


14.0 


— 


421 ; 15 


421 1 — 


431 


IS 1 204 , — 


447 


15 


864I — 


403 


IS 


22.0 


— 


422 15 


183 1 - 


432 


IS 1 140 1 — 


448 


15 


6881 — 


408 


15 


21.3 


— 






433 


IS ' no ; ^ 


449 


IS 


502 — 


Ave. 


15 


19.0 


100 


Ave. 15 


302 


100 


Ave. 


15 151 100 


Ave. 


15 


685 100 


411 


20 


16.8 




424 20 


341 


— 


434 


20 159 — 


450 


20 


1647' — 


412 


20 


26.4 


• — 


425 20 


183 


— 


435 


20 222 — 


451 


20 


242 — 


430 


2D 


54-9 


— 








436 


20 186 — 


452 


20 


801; — 


Ave. 


20 


32.7 


173 


Ave. 20 


262 


87 


Ave. 


20 182 132 


Ave. 


20 


896 131 


415 


25 


74-4 


— 


426 25 


496 


— 


437 


25 522 — 


453 


25 


697 — 


416 


25 


26.8 


— 


427 25 


130 


— 


438 


25 164 — 


454 


25 


485 — 


417 


25 


37-2 


• — • 








439 


25 244 


455 


25 


454 — 


Ave. 


25 


46.1 


242 


Ave. 25 


313 


103 


Ave. 


25 310 205 


Ave. 


^5 


545, 80 


418 


30 


78.0 


— 


428 : 30 


767 


— 


440 


30 405 — 


456 


30 


560 — 


419 


30 


61. 5 


— 


429 30 


83 




441 


30 j 193 1 


457 


30 


752! — 


420 


30 


26.4 


— 








442 


30 339 — 


458 


30 


432; — 


Ave. 


30 


55-3 


290 


Ave. 


30 


429 


134 


Ave. 

443 

444 
445 


30 312 1 205 

40 372 , — 
40 - — 
40 185 — 


Ave. 

459 

460 


30 

40 
40 


5811 85 

760 — 
752 — 


















Ave. 


40 278 184 


Ave. 


40 


756 no 



Why the lowering of the moisture content in the unplanted series 
had no effect is hard to explain, as an aeration of the soil under the 
low water content would be expected to increase the nitrates, yet it is 
evident that the results are influenced by other factors which tend to 
equalize this eff'ect. 

It was thought that a study of the nitrate-producing power of the 



64 



JOURNAL OF THE AMERICAN SOCIETY OF AGRONOMY, 



soil mig'ht throw some light on the effect of drying soil on the nitrify- 
ing organisms of the soil. At the time the nitrates were determined 
in the soil, another loo-gram sample was taken, placed in a bottle, 
plugged with cotton, and incubated for seven days at 30° C. Nitrate 
determinations were then made as shown in Table 7. 

A com])arison of the nitrates in the soil as shown in Table 6 with 
the nitrates after incubation as shown in Talile 7 will show that in 
nearly all cases denitritication has taken place. It can be seen from 
the tables that the variation in the samples from pots under the same 
treatment are too great to warrant any conclusions on the eft'ect of 
lowering the moisture content on the power of the nitrifying organisms 
of the soil. 

Table 7. — llffrcl of Prczioiis Moisture Coiitciif on Xitnitcs Produced by Incu- 
bation for Sci'cn Days at 5"° C. 







s 


.il No. I. 












g 


oil Nc 


. 2. 








Series i, Planted. 


Series 2. I 


nplanted. 


Series i, Planted. 


Series 2, Unplanted. 




2 5 




(^ 


A 


'> 1; 


^ 





6 


CL, 




a 
Z 




a 

X 


2, 


|'-3 




c 




£ - 








" " 








Ch " 






— 




1 


P. 


P- P- 






P. 


p. p. 






p. 


p. p. 






p. 


P- P- 




Cl. 


m. 






cl. 


in. 






Ct. 


m. 






cl. 


in. 


401 


T5 


30 


— 


421 


15 


240 


— 


431 


15 


124 


— 


447 


15 


433 — 


403 


15 


04 


— 


422 


15 


— 


— • 


432 


15 


144 


— 


448 


15 


(172 — 


408 


15 


56 


— 








433 


15 


88 


• — 


449 


15 


672 — 


Ave. 


15 


53 


1 00 


Ave. 15 


240 


100 


Ave. 


15 


118 


100 


Ave. 


15 


593 100 


411 


20 


59 


— 


424 


20 


222 


— ■ 


434 


20 


264 


— 


450 


20 


1 152 — 


412 


20 


48 


— 


425 


20 


184 


— 


435 


20 


170 


— 


451 


20 


370 — 


430 


20 


34 


— • 










436 


20 


96 


— • 


452 


20 


704 — 


Ave. 


20 


47 


89 


Ave. 


20 


203 


84 


Ave. 


20 


178 


153 


Ave. 


20 


778 131 


415 


25 


3 7 


— 


426 


25 


200 


— 


437 


25 


200 


— 


453 


25 


60S 


— 


416 


25 


34 


— 


427 


25 


160 


— 


438 


25 


144 


— 


454 


25 


576 


— 


417 


2S 


40 


— 










439 


25 


168 


— 


455 


25 


336 — 


Ave. 


25 


3 7 


70 


Ave. 25 


iSo 


75 


Ave. 


25 


171 


145 


Ave. 


25 


507 85 


418 


30 


50 


— 


42S ' 30 


21 


— 


440 


30 


352 


— 


456 


30 


480 — 


419 


30 


34 


— 


429 


30 


84 


— 


441 


30 


7-^6 ; — 


457 


30 


572 


— 


420 


30 


50 


— 








442 


30 


360 


— 


458 


30 


448 


— 


Ave. 


30 


44 


83 


Ave. 30 


52 


20 


Ave. 


30 


329 


278 


Ave. 


30 


500 


84 


















443 


40 


144 


— 


459 


40 


528 


— 


















444 


40 


— 


— 


400 


40 


526 


— 










i 






445 


40 


152 


— 


























Ave. 


40 


148 


125 


Ave. 


40 


527 


89 



Pofassiiiiii, Cah'iitiii, and fliosfiJionis. — Determinations were made 
of the potassium and calcium in the water e.xtracts and of the phos- 



KLEIN : STUDIES IN THE DRYING OF SOILS. 



65 



Table 8. — Effect of Previous Moisiure Conient on the Fotassium, Calcium and 
Phosphorus in the Soil. 



Series i. Planted. 



Series 2, Unplanted. 



Pot Nc 



Previous ] 
Moisture 
Content. 



Ca. 



Pot. No. 



Previous 

Moisture 
Content. 



K. 



Ca. 



Lime 
P2O5. R.(Squired 
(CaO). 











Soil No. i 








• -. 






p. p.m. 


p. p.m. 






p. p.m. 


p. p.m. 


p. p.m. 


p. p.m. 


401 


15 


42.2 


9.0 


421 


IS 


12.0 


18.5 


— 




403 


•IS 


21.3 


12.2 


422 


15 


43-1 


21.4 


13.7 




408 


IS 


12.6 


10. 1 














Ave. 


15 


23-3 


10.4 


Ave. 


15 


27-5 


20.0 




411 


20 


30.4 


7-3 


424 


20 


14.7 


21. S 


— 




412 


20 


21. 1 


13.6 


42s 


20 


41.8 


25-4 


I3-I 


* 


430 


20 


II. 7 


II. 8 














Ave. 


20 


21. 1 


10.9 


Ave. 


20 


27.6 


23-4 


— 


0) 


415 


25 


21.3 


9-7 


' 426 


25 


16.4 


20.3 


— 





416 


25 


■ II. 6 


12. 1 


427 ' 25 


20.3 


18.8 


14.6 




417 


25 


26.4 


8.6 . 










, 


Ave. 


25 


19.8 


10. 1 


Ave. 25 


18.3 


19.6 


— 




418 


30 


24.4 


— 


428 1 30 


12.7 


22.0 


— 




419 


30 


21.4 


14.6 


429 30 


32.3 


12.6 


15.0 




420 


30 


22.2 


8.4 












Ave. 


30 


23-7 


II. 4 


Ave. 30 


22.5 


17-3 


— 













Soil 


No. 2 










431 


15 


28.3 


I3-I 


447 


IS 


74-4 


23.2 


14-3 


1,400 


432 


15 


19.2 


17.6 


448 


15 


84.2 


27.1 


— 




433 


15 


62.2 


9.9 


449 


15 


60.0 


29.6 


— 




Ave. 


15 


36.6 


13-5 


Ave. 


15 


72.6 


26.6 


— 


— 


434 


20 


38.4 


19.0 


450 


20 


144-3 


32.7 


13-4 


1,100' 


435 


20 


29.6 


I5-I 


451 


20 


84.4 


18.6 


— ■ 


— 


436 


20 


34-3 


14.6 


452 


20 


55-8 


32.3 


— ■ 


— 


Ave. 


20 


34-1 


16.2 


Ave. 


20 


91-5 


27.9 


— 


— 


437 


25 


14.6 


17-3 


■453 


25 


104.0 


27-5 


18. 1 


1.275 


438 


25 


29.0 


13-4 


454 • 


25 


41.6 


19.8 


— 


■ — 


439 


25 


38.1 


20.3 


. 455 


25 


111.3 


25.0 


— 


— 


Ave. 


25 


27.2 


17.0 


Ave. 


25 


85.6 


24.0 


■ — ■ 


— 


440 


30 


45-2 


21.0 


456 


30 


112. 


22.8 


II. 8 


1,200 


441 


30 


61.0 


17.2 


457 


30 


61.8 


25-9 


— 


— 


442 


30 


41.4 


22.8 


458 


30 




24.9 


— 


— ■• 


Ave. 


30 


49.2 


20.0 


Ave. 


30 


86.9 


24-5 


— 


— ■ 


443 


40 


22.9 


19.4 


459 


40 


96.6 


24.8 


15.2 


1. 075 


444 


40 


105.2 


13-4 


460 


40 


79.0 


27.0 


— • 


• -^ 


445 


40 


9.2 


12.3 














Ave. 


40 


46.4 


15.0 


Ave. 


40 


87.8 


25-9 







phorus in a fifth-normal nitric acid extraction of the soils. The cal- 
cium was determined by the turbidity method and the potassium by 
the colorimetric method of the Bureau of Soils.'- The phosphorus 

3 Schreiner, Oswald, and Failyer, George H., Colorimetric, Turbidity and 
Filtration Methods Used in Soil Investigations, U. S. Dept. Agr., Bur. Soils 
Bui. No. 31. 1906. 



66 JOURXAT, OF THE AMERICAN SOCIETY OF AGRONOMY. 

was determined colurinietricall}' according to the metliod of Fraps.'* 
The results are sliown in Talkie 8. 

From a study of Table 8 it may be seen that there has been very 
little effect due to the different moisture contents. A reduction of 
the potassium and the calcium was found in the planted series of 
soil Xo. 2. The ])hosphorus was determined in the unplanted series 
of bodi soils and no differences were found due to differences of 
moisture content. 

It must l)e concluded from these data that the reduction of the 
'moisture content has no ai)i)recial)le eff'ect on the potassium, calcium, 
ajid pho'sphorus in the soil. 

Lime Rcqnircnicut. — In order to determine whetlier the lowering 
of the moistm-e content hatl any effect on soil aciditv, lime re<|uirement 
deterniinaticms were made according to the metliod of liizzell.^ These 
results are presented in Table 8. The cla\- loam shows no lime re- 
quirement, the organic clay loam an average of i,200 p. p.m. CaO. 
No difjferences are shown i\uQ to the lowering of the moisture content. 

Sininiiary oj' ILvhrriiiicnt i. 

1. The drying of soil prexious to planting has a Ijeneficial effect on 
plant growth. 

2. The factor \\hich causes this bencticial condition due to drying 
is affected by the organic matter in the soil, as is shown from the 
results of the two soils used, which differ onl\' in organic content. 

3. The j)revious dr_\ing of the soil has no eff'ect on the total nitrogen 
in the dry matter of the crop. 

4. The \vater-solul)le matter is increased in the clay loam with a 
drying out of the soil, while in the same stjil with a high organic con- 
tent the opposite result occurs. The organic content nnist be the de- 
ciding factor. 

5. In the planted series of l)Oth soils a decrease in the previous mois- 
ture content has re<idted in a decrease in the nitrates in the soil. In 
the unplanted series no eitect has been found. 

A denitrification \\as fotmd in the soil samples when incubated at 
30" C. for seven (la\s. The great A'arialion in the test allows no con- 
clusions from the effects of drying the soil. 

6. The drying out of the soil has little ettect on the availa])le potas- 
sium, calcium, or jihosphorus in the soil. 

•* Fnips. G. S., Active Pliosplioric Acid and Its Relations to tlie Needs of 
the S<'\\ for T'hosplioric .\eid in Pot Exiieriments, Tex. Asr. I'^xp. Sfa. Bnl. 

No. 126, lOOi) flOH) ). 

^Bizzell, J. -A., and Lyon. T. L., Estimation of the Lime Requirements of 
Soils, Journ. Indus, l^ni^in. C'hem., 5: ]oii-U)i2, 1013. 



klein : studies ix the drying of soils. 6/ 

Experiment 2. Tjie Effect of Drvixg a Soil on its Physiolog- 
ical Condition as jNIeasured by the Carbon Dioxid 
Production axd Nitrification. 

As a study of the effect of drying and wetting a soil on its bacterial 
activity, the carbon dioxid formation has been determined. A study 
of the effect on nitrification has also been made by determining the 
nitrates in the soil and its nitrifying power. It has been shown by 
previous investigators that the bacterial activity of the soil may be 
measured by the carbon dioxid production. It can not be said that 
this determination gives a complete measurement of the bacterial ac- 
tivity, yet sufficient data have been obtained to show that the effect of 
drying a soil on its bacterial activity may be determined in this way. 
As a check on the carbon dioxid deteriuination and because of the 
importance of the nitrifying organisms, the nitrates and the nitrifving 
power were determined. 

AMien the pots that had been kept in the field-house for two months 
were returned to the greenhouse, it was found that a number of them 
had been broken. The clay loam (soil No. 1) from six of these 
broken pots was transferred to new pots, and the soil brought to an 
optimum moisture content. 

After the pots were held at an optimum moisture content for four- 
teen months, they were sulimitted to a treatment as shown in the 
following i)lan : 

Pot I. Original soil. Determinations made on wet soil. 

Pot 2. The soil taken from the pot and dried in the drying room at ,30-35° C. 
for ten days and determinations made on the dry soil. 

Pot 3. Soil dried as above, but it was again brought to an optimum water con- 
tent (25 per cent.) and held fur sixteen days before deter-minations 
were made. 

Pot 4. Treated as [xit 3. Iiut lield thirty-five days l)efore determinations were 
made. 

Pot. 5. Treated as pot 4, but again dried and lield eleven days at optimum 
moisture content before making determinations. (Two dryings.) 

Pot 6. Treated as pot 5, but again dried and wet again fourteen days before 
making determinations. (Three dryings.) 

Carbon Dioxid Produced on Drying and JJ'cttiug a Soil. 

The methofl used to study the amount of carlxin dioxid produced in 
a soil was a modification of Stoklasa.'' .\ diagram and description 
of the apparatus is presented in figure 3. 

The soil sample was well mixed and 500 grams (on drv basis) 
placed in the glass cylinder. The cylinders were kept in an incubator, 

^Stoklasa, J., in Handlnich der Biochemischen Arbeitsmelhoden (Alber- 
halden), Band 5, Teil 2, p. 869, 1012. 



68 



JOURNAL .OF THE AMERICAN SOCIETY OF AGRONOMY. 



held at a temperature of 30° C. The air free of. carbon dioxid was 
drawn through the soil in the cyHnders, the rate .of flow being regu- 
lated at " k " on the aspirator. By making some preliminary experi- 
ments the maximum rate of flow necessary was found. The carbon 
dioxid produced was measured daily for ten da}s, except in the case 
of the air-dry soil, which ceased production after the seventh day. 
Air determinations were made in triidicatc. The results for each 
soil are presented in Table 9. 

Table 9. — Daily Frodiictiflii of Carbon Dioxid in Paris per Million from a Soil 
J'ariouslv Treated as to Moisture Content. 









Parts per Million 


of Carbon Dioxid. 






Sample No. 


Day. 






I 2 


3 


4 56 


7 8_ ' 9 


10 


Total. 



Pot I. Orieinal Soil— Not Dried. 



I 


.S4'J 


206 


76' 


92 


120 


88 


"52 


64 


198 


234 


1,676 


2 


542 


216 


104 


104 


86 


162 


— 


152 


92 


140 


1,598 


3 


546 


112 


116 


72 


74 


122 





204 


72 


— 


1. 318 


Average 


544 


178 


99 


90 


93 


£24 


26 


140 


120 


187 


1,601 



Pot 2. Soil Dried and NofWet Again. 



I 


108 


8 





68 1 


4 











— ! — 188 


2 


84 


16 





46 


10 





32 





— ' — 188 


3 


54 


108 


4 


40 


■ 44 


30 


30 





— - ; — 1 310 


Average 


82 


44 


I 


51 


19 


ID 


20 





— — 229 





Pot 3 


. Soi 


1 Dried and Wet 


again for 


Sixteen Days. 




I 


396 


228 


174 


246 


158 


224 


276 


I 236 


164 268 


2.370 


2 


328 


316 


184 


208 


58 


206 


294 


52 


168 158 


1.972 


3 


648 


104 


184 


232 


68 


220 


252 


; 96 1 68 1 188 


2.160 


Average 


457 


216 


181 


228 


94 


217 


274 


' 128 166 1 205 


2,166 



Pot 4. Soil Dried and Wet again for Thirty-five Days. 



Average. 



486 


276 


216 


216 


240 


240 


132 


168 


24 





1.998 


200 


220 


224 


186 


224 


162 


2 


62 


164 


124 


1. 561 


128 


244 


140 


156 


244 


178 





74 


142 


30 


1.336 


271 


247 


193 


186 


236 


193 


45 


roi 


no 


S3 


1.635 



Pot 5. Soil Dried Twice and Wet again for Eleven Days. 



Average. 



I 260 

1 1 1 1 2 

686 



554 
402 
478 



202 


168 


1.96 


374 


164 


682 


1 288 


166 


439 



166 

66 
116 



142 
196 
169 



166 I — i — 
76 , — , — 



1.854 
3,072 



— — 2.463 



Pot 6. Soil Dried Three Times and Wet again for Fourteen Davs. 



Average. . . 



414 


296 


186 


6 


4-00 


600 


284 


322 


262 


244 


507 


290 


254 


134 


322 



160 I 100 

204 162 
182 131 



152 

no 



216 

264 
243 



276 2,206 
190 2,642 
233 2,427 



l\v a study of the tables it will be seen that the bacterial activity was 
greatlv increased by a previous dr^'ing of the soil. In the soil that 



KLEIN : STUDIES IN THE DRYING OF SOILS. 



69 



was not wet again after drying, the bacterial activity was greatly 
inhibited, and after seven days the carbon dioxid production had com- 
pletely stopped. 

One drying of the soil greatly increases the activity over the orig- 
inal soil. In the soil held at an optimum moisture content for 35 
days after drying the production of carbon dioxid becomes normal 
again, as shown by a comparison' of Pots i and 4 (Table 9). A soil 
dried twice does not show a much greater activity than when dried 
once, while three dryings show no increase over two dryings. Evi- 
dently the factor that causes the increase is not greatly affected after 
the first drying of the soil. 



Tlie Effect of Drying and ll'cffiiig a Soil on the Nitrates and 
■ Nitrifying Power. 

The nitrates were determined colorimetrically in a water extract of 
the sample by the phenol disulphonic-acid method. Samples from each 
pot were taken at the time the carbon dioxid determination was made, 
one part being used for the immediate determination of the nitrates 
and the other for the determination of the nitrifying power. The 
nitrifying power was determined by incubating the samples for seven 
day at 30° C. The results are sliown in Table 10. 






Fig. 3. Apparatus for determination of the carbon dioxid produced in a soil. 
Description of apparatus: a. Incubator; b. wash-bottle containing Ba(OH)^: 
c, wash-bottle containing KOH ; d. glass cylinder containing soil ; c, U-tube 
containing H2SO4 ; /, U-tube containing CaCL; g. pntash bulb; /;, U-tube con- 
taining. CaClc; i, U-tube containing H2SO4 ; /, aspirator bottle; J;, stop-cock for 
regulating flow of air; t, thermometer; iv, glass-wool in bottom of cylinder; 
y, thermostat. 



JO JOURNAL OF THE AMERICAN SOCIETY OF AGRONOMY. 



Tablf- 10. — Effect of Drying and U'eitiiuj a Suil on the Xitratcs and Xitrifying 

Poi.'cr. 





Parts per INIillion of Nitrates in : 






1 Soil Dried Soil Dried 




c 




Ten Days, Ten Days, 




Oriicinal 


Tlien ' Then 


Soil I reated ^^^ jvJq „ 
„r;^ ^'"- f- , '''hen I'ried 




Si.il at 25 


Co-1 Dried ••'"'"iMlit to 1 P.roii.t;ht to 


"o. 


Ten Days. , 25 Percent , 25 Percent 


f,hen Dried t,,^. i-hird 


S 


Moisture 


Dry Soil ! >'"iS'ture .Moisture 
(]>,, ,, iC'ontent and i( onte]U and 


^.f" ,?>'^' 1 'J'' me and 






IhenM-et 1 ^ct Four- 




(Put I). 


^ iHeldforSiv;- HeldThiity- 


Eleyen Days ,^.^„ j) 






' teen Days fiye Days 


(Pots). (Pot 6). 






(Pot 3). (Pot 4). 





Nitrates in the Soil 



Nitrif3ing Power after Inctibation for Seven Days at 30° C. 



Series i, 



Series 2, 



Series 3, 



Soil alone : 

1 208 

2 I 200 
Ave. ' 204 

Soil +2 gr. dried bl 

1 192 

2 lOo 
Ave. 176 

Soil +0.5 gr. (NH4) 



172 

ood : 
22S 
200 
214 

2CO:!: 



184 
162 



208 
216 

212 



i3(' 
136 
136 



336 
304 



368 
384 
376 



400 
400 
400 



I 


140 


143 


117 


166 


264 


328 


2 


160 


133 


117 


166 


2 5^J 


336 


Ave. 


150 


138 


117 


166 


260 


332 



400 

384 

39-' 

464 
432 
448 



1 


224 


190 


232 


2S8 


672 


416 


2 


208 


22S 


224 


304 


640 


416 


Ave. 


216 


209 


228 


296 


656 


416 



]'"irst considcrini:^ the effects on tlie nitrates, we find that the 
(h\\Tng of the soil has greatly re(hice(l them, and as has lieen prev- 
ionsly shown also has rednced the car])on dioxid |)roduction. The 
revvetting of the dry soil for a period of sixteen days has fm'ther de- 
creased the nitiilication. in this sani])]e the opposite is found in the 
carhon dioxid production. In the soil held moist for thirty-tive da}S 
after one drying and in those previously dried twice and three times, 
;m increase in nitrification is found. This increase corresponds with 
the carhon dioxid ])roduction in these samples. \\'hy samj^lc 3 has 
shown a decrease is not altogether clear. 

'Jdie restdts from the nitrate determinations as compared with the 
carbon dioxid production show that the nitrification as effected hy the 
drying of the soil is for tlie mo^t ]>arl l.uological, hut there must he 
factors other than biological which inlluence this change. These will 
i)e discussed later. 

The nitrifying ])Ovver of the soil was determined in three series in 
order to obser\-e the effect of the addition of organic and inorganic 



KLEIN: STUDIES IN THE DRYING OF SOILS. J I 

nitrogen on nitrification. Samples of loo grams of soil were used in 
each cas^. The three series were as follows: 

Series i. Untreated. 

Series 2. 2 grams of dried l)lood added to the sample. 

Series 3. c.5 gram of (NHijSO^ added to the sample. 

It will be seen from Table 10 that the addition of nitrogen either in 
organic or inorganic form has increased the nitrification. However, 
the results from each treatment as compared with the nitrates before 
incubation show, in the main, the same order of difl:'erence. 

Considering the efi:'ect of drying of the soil on the nitrifying power, 
the original soil shows an increase of 54 p. p.m. when the soil has been 
incubated alone. Series 2 and 3 of the same sample gave an increase 
of 26 and 66 p. p.m. respectively. In the dry soil the nitrates are in- 
creased in about the same ratio, but here there is an error due to the 
wetting of the soil on incubation, and the same results are obtained as 
in sample 3. If the nitrifying power of the dry soil had been deter- 
mined, it is very proljable that no nitrifying power would have been 
obtained. In sample 3 there was an increase of 55, 95, and 11 1 p. p.m. 
in series i, 2, and 3 respectively. This shows that the effect of prev- 
iously drying a soil is tO' increase the activity of the nitrifying organisms. 
In sample 4 the incubation of the soil has shown a decrease, but an 
increase of 138 and 130 p. p.m. was found in series 2 and 3 of this 
sample. In the carbon dioxid determination the rewetting of the 
soil for a period of thirty-five days gave a result similar to the orig- 
inal soil. Soils dried two and three times have increased the nitrify- 
ing power over the samples dried once. From the table it can be seen 
that the maxinumi is reached at two dryings. These results would 
show that the activity of the nitrifying organisms is increased liy a 
previotis drying of the soil, Init reaches a maximum at two dryings. 

Sitniiiiarx of Experiment 2. 

1. The bacterial activity as measured by the carI)on dioxid produc- 
tion is increased by a previous drying of the soil. 

2. The carbon dioxid production is very low in a dr}- soil, the pro- 
duction ceasing after seven days. 

3. The activity is increased by two dryings, the third drying show- 
ing only very slight increase over the second. 

4. A soil held moist for thirty-five days after one drying assumes its 
normal condition, the activity being only slightly greater than in the 
original soil. 

5. The previous drA'ing of the soil increases nitrification. 



']2 JOURNAL OF THE AMERICAN SOCIETY OF AGRONOMY. 

6. The dry soil shows a reduction in nitrates, as in the carbon dioxid 
])roduction. 

7. The nitrilication is increased by two dryings and again in the 
soil dried three times. 

8. The nitrifying power ol the soil is increased by a previous drying. 

9. The nitrifying power continues to increase witli two dryings, 
Init prblialjly reaches its maximum at three dryings. 

10. The ettect of adding organic or inorganic nitrogen to the 
samples is shown by a marked increase in the nitrates produced. The 
increase in the determinations is in the same ratio as in the sample 
with no nitrogen added. • ■ - 

Discussion and Conclusions. 

The foregoing results show that the drying of soil has an effect 
on its fertility, which results in an increased plant growth. The crop 
growth is increased by a previous lowering of the moisture content, 
but the diiterence in the organic content as shown in the two soils 
used, has influenced the changes which are produced. 

In Experiment i there is a drying out of tlie soil by a lowering 
of tlie moisture content, but in no case do we have a soil completely 
air-dried. This experiment represents a condition that takes place in 
a humid region where the soil rarely reaches an air-dry condition. In 
a consideration of the results from Experiment i this must be kept in 
mind. 

While the effects of drying on the physical changes have not been 
delmitely studied, a discussion of the subject will necessarily include 
the ph}\sical factors which are acting through a change in the soil 
moisture. 

The drying out of the soil increases the granulation, which is in the 
most i)art due to an alteration of the colloidal material. The increased 
graiuilation allows a greater amount of soluble salts to be carried in 
the granules, which on subsecjuent wetting allows a greater amount to 
go into solution. Referring to the results obtained on the amounts of 
water soluble material found in the two soils under diiferent mois- 
ture contents, we find that the drying out of the clay loam has caused 
an increase in the water soluble material, while in the organic clay 
loam the opposite occurs. As these soils differ only in the organic 
contc-nt. the factor which influences the solubility of the soil constitu- 
ents nnist be due to the dift"erence in the organic matter of the two 
soils. If in the clay loam a granulation due to drying has caused a 
greater alteration of the colloidal material, this would allow the water 
greater access to the soil particle; and if the concentration of the salts 



KLEIN: STUDIES IN THE DRYING OF SOILS. 73 

on the surface of the particle has resulted from an increased film 
■pressure around the particle, a greater amount of soluble material 
will be recovered by a subseciuent wetting of the soil. However, in 
the organic clay" loam the decrease found in the soluble matter on 
drying would tend to show-that the great amount of material soluble 
when the soil is held at high water content overcomes any increase 
that may be due to a drying of the soil. 

Again, as the organic clay loam shows a lime requirement of 1,200 
p.p;m. CaO, the acidity which is due to the organic matter would 
deflocculate the colloidal material, resulting in a less amount of surface 
being exposed to the solvent than in the clay loam. It has been 
shown by previous investigators that a soil high in organic matter has 
a great absorptive power. This ab.sorptive power would increase the 
plant food held by the soil and result in an increase of the soluble 
matter when the soil was dried; but if the soil was not dried to a low 
enough water content to alter this absorptive power, no increase would 
result'. The resinous and fatty material of the organic matter may 
surround the mineral particles anil allow no greater solubility even if 
more soluble salts are -exposed to the solvent after a drying of the soil. 
It has been considered by some investigators that the water-soluble 
material forms a colloidal film around the soil particle. On drying a 
soil this film will be altered and allow a greater solubility of the sol- 
uble salts. This may partly account for the increase in the 
water-soluble material in the clay loam when dried to a 15 percent 
moisture content, but in the organic clay loam it may be that the large 
amount of organic matter soluble would strengthen this colloidal film 
and a greater drying be necessary to alter the pressure of the film. 

Other factors, mainly chemical, must be considered in a discussion 
of the effects of drying soil. The dehydration of the silicates, deoxi- 
dation of the oxids, and oxidation of many of the compounds are some 
of the important chemical changes which take place in the soil on 
drying. However, in Experiment i the soil has not been dried below 
a moisture content of 15 percent, and these factors cannot exert any 
marked influence on the changes produced. 

The drying out of the soil causes an increase in the nitrification in 
the planted series, but no efi'ect is observed in the unplanted series. 
Why this occurred is not clear. The biological factors that are at 
work here may sufficiently alter the results so as to eliminate any 
diiference due to the changes in moisture. This will be discussed 
further under the results of Experiment 2. 

Turning to the determinations of potassium, calcium, and phos- 
phorus, as afl:'ected by the lowering of the moisture content, it was 



74 JOURNAL OF THE AMERICAN SOCIETY OF AGRONOMY. 

found that there is no increased solubihty of these elements. This 
would show that the beneficial eifect on plant growth must be due 
to a great extent to an alteration of the ])hysical condition of the soil 
and not to a greater amount of plant food being liberated. 

'J1ie results from Experiment i show that the lowering" of the 
moisture content ]>revious to planting has a beneficial efi:'ect on plant 
growth. ( )f the changes produced in the soil, tlie physical, chemical, 
and l)iological factors nnist be considered, but in the results obtained 
from Ex])eriment i, it would seem that the change in the physical con- 
dition is the iM"incipal factor. 

In Experiment 2, iItc results of drying a soil are studied in connec- 
tion with the l)ioIogical changes. The eilects on the biological factors 
have been measured by the l)iochemical changes produced. This ex- 
periment difil'ers from ]^xi)eriment i in that the soil was dried in a tlry- 
ing room at a temperature (')f 30° C. and ma_\" be considered as air- 
dried. 

T>efore discussing the eftects of drying on the [jhysiological changes 
produced as measured !»>■ the carl)on diijxid production, it will be well 
to consider whether the carbon dioxid produced is a correct measiu'e 
of the I)acterial activity. The most important objection to this method 
is that the amount ol)tained in some cases a])pears to be too high to 
attri])ute to bacterial action. The chemical changes produced on dry- 
ing may be partlv res])onsil)le for the increase in carljon dio.xid. 
It can not l)e s.aid that all the organisms in the soil evolve carbon 
dioxid: ])ut if the most important soil organisms produce carbon 
dioxid and if the changes jirodnced 1)\' dr\ing act similarly on these 
organisms, the measuring of tlie carlion dioxid ])roduction should 
give a relative measurement of the ])aclerial activit\. 

The results of the experiment show that a prex'iously dried soil 
gives a greater bacteri.al activity as measured b)- the carbon dioxid 
production and nitrification in the soil. There are a number of pos- 
sible reasons to be considered in a discu-sion of the efi:'ect of drying on 
the i)hysiological condition of the soil. 

It has ])een shown l)y mrmy investigators that the organisms in the 
soil. excei)t the nitrificrs, ;ire resistant to drying. If the nitrifying 
organisms are destro\ed on drying the soil, then the increased nitrifi- 
cation must l)e accounted for through chemical changes produced in 
the soil. The drying of the soil alters the colloidal material and allows 
a greater amount of oxygen to enter the soil. After the soil has been 
wet again an increa.-e is found in the nitrates, which would lie due to 
the induced oxidatirtn. 

1 1 in drying a soil a greater .amount of |)laiU food is made available, 



KLEIN: STUDIES IN THE DRYING OF SOILS. 75 

the bacteria would be able to obtain a greater supply of food. Ac- 
cording to Greig-Smith, the drying of the soil would destroy the 
vva.xy substance surrounding the soil particle and allow the more re- 
sistant bacteria a greater food suppl} . 

The resistance of the organisms to drying may be due to the 
formation of spores. As it is known that the nitrifying bacteria do 
not produce spores, we may consider that the decrease in the nitrify- 
ing organisms and the increase of the other organisms on drying may 
be due to the ability of the latter to form spores, in a discussion 
of the causes of the beneficial efiect due to drying it is necessary to 
consider the h}pothesis of Russell and Hutchinson. Considering that 
the drying of the soil is a partial sterilization, they believe that the 
drying of soils destroys or inhibits the action of the phagocytic or- 
ganisms, and an increase in the ammonifying bacteria results, which 
is beneficial to the productiveness of the soil. 

In an air-dried soil the hygroscopic water may be sufficient to satisfy 
the requirements of the bacteria. The hygroscopic water is held 
around the soil particle as a thin film. This film exerts a very great 
pressure, which, it seems, would not allow the organisms to obtain the 
water or the food enveloped in it ; but if the bacteria themselves were 
included within this film, then sufficient food might be obtained. 

From the results obtained in this investigation and by other workers 
it would seem that the increase in bacterial activity on drying a soil is 
not a question of bacterial numbers, l)Ut depends upon the relative 
resistance of the important soil organisms. 

In a consideration of the efifect of drying a soil on the physiological 
condition of the soil, no definite conclusions can be drawn until more 
knowledge is obtained relating to the eltect on the difi'erent groups of 
organisms. The sul^ject is very complex and must include many 
factors both chemical and physical, as. for example, an alteration of 
the colloidal material which would allow a greater oxidation. 

The results of these studies show that the drying of soil afl^ects the 
physical, chemical, and biological factors, resulting in an increased 
plant growth. The increased crop growth on a soil that has been 
previously dried is of importance to the practical (luestion of soil 
management, more especially in the arid regions where the soil is often 
air-dried. 

Bibliography. 

Cameron, F. K., and Gallagher, ¥. E. 

1908. Moisture Content and Physical Condition of Soils. C. S. Dept. of 
Agr., Bur. of Soils Bui. 50: 7-70. 



76 JOURNAL OF THE AMERICAN SOCIETY OF AGRONOMY. 

Fippin, E. O. 

lOio. Some Causes of Soil Granulation. Proc. Amer. Soc. of Agron., 2: 
106-121. 
Fisclicr, Hugo. 

1012. \'om Trocknen dcs Bodens. Ccntbl. Bakt. II: 36: 346-340. 
Circis-.Smitii. 

igii. The Bactcriotoxin.s and Agriccre of Soils. Centbl. Bakt. II: 30: 
1 54- 1 :S. 
Howard, A., and Howard, G. L. C. 

1007. The Fertilizing Effect of Sunlight. Nature (London), 82: 2103:456. 
Kelley, \\'. P.. and McGeorgc, W. 

1013. The Eft'ect of Heat on Hawaiian Soils. Hawaii Agr. Expt. Sta. 

Bui. 30 : 5-38. 
King, F. H. 

1905. Investigations in Soil Management. V. S. Dept. of Agr., Bur. of 
Soils Bui. 26: 13-205. 
Leather, J. \\\ 

1912. Records of Drainage in India. Mem. of the Dept. of Agr. in 
India, 2 : 63-140. 
Lyrtn, T. "L., and Bizzell, J. A. 

1013. Some Relations of Certain Higher Plants to the Formation of Ni- 
trates in the Soils. Cornell Univ. Agr. Expt. Sta. Mem. i : 9-1 11. 
Pickering, .S. U. 

1908. Studies nn ( iermiriation and Plant Growth. Jour. Agr. Sci. 2; 

4II-43-1- 

1908. The Action of Heat and .Antiseptics on Soils. Jour. Agr. Sci. 3: 

33-54- 
Rahn, Otto. 

11)07. P.akteriologische Untersuclnmgen liher das Trocknen des Bodens. 
Centlil. Hakt. II : 20: 3S-61. 
Richter, L. 

1806. UI)cr die Ver;inderung whelche der Boden (lurch der Sterilisieren 
erleidt't. Landw. \'ers. Stat. 47: 26i>-274. 
Kitter, G. W. 

1912. Das Trocknen der Erdcn. Centlil. Bakt. II: 3,}: 116-143- 
Russell, E. J. 

1910. The Fertilizing Effect of Sunlight. Nature (London), 83: 2105: 6. 
Russell, E. J., and Hutchinson, H; B. 

1909. The Fff(-ct of Partial Sterilization of Soil on the Production of 

Plant F.iod. J(_)ur. Agr. Sci. 3: 111-144. 

1913. Ibid. Jour. Agr. Sci. 5: 152-221. 
Russell, E. J., and Petherhridge, F. R. 

1913. On the Grijwtii of Plants in Partially Sterilized Soils. Jour. Agr. 
Sci. 5: 248-2^7- 
Russell, E. J., and Smith, N. 

1905. On the Question whether Nitrites or Nitrates are Produced by Non- 
liacterial Processes in the S(^il. Jour. Agr. Sci. i: 444-453. 
Sharp, L. T. 

1913. Some Bacteriological Studies of Old Soils. The Plant World, 16: 
loi-l 15. 



KLEIN: STUDIES IN THE DRYING OF SOILS. 7/ 

Warrington, R. 

1882. Determination of Nitric Acid in Soils. Jour. Chem. Soc. Trans., 
1882: 351. 
Wollny, E. 

1897. Untersuchungcn iil^er der Volumveninderungcn dcr Bodenarten. 
Forsch. auf d. Geb. Agr.-Pliys., 20: 2: 14. 

Acknowledgment. 

The writer desires to acknowledge his profound gratitude to Pro- 
fessor T. L. Lyon, under whose inspiration and direction these results 
have been accomplished; also to Professor W. A. Stocking, Jr., for 
valuable assistance in connection with the bacteriological methods 
used. 



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